Public attributes in Python - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of accessing a public attribute

What is the output of this code?

Python

class Car:
    def __init__(self, brand):
        self.brand = brand

my_car = Car('Toyota')
print(my_car.brand)

A AttributeError

B car.brand

C None

D Toyota

💡 Hint

Public attributes can be accessed directly using the object name.

The attribute 'brand' is public and set in __init__. Accessing my_car.brand prints 'Toyota'.

❓ Predict Output

intermediate

Changing a public attribute value

What will be printed after changing the public attribute?

Python

class Person:
    def __init__(self, name):
        self.name = name

p = Person('Alice')
p.name = 'Bob'
print(p.name)

A Alice

B None

C Bob

D AttributeError

💡 Hint

Public attributes can be changed directly.

The attribute 'name' is changed from 'Alice' to 'Bob'. So printing p.name outputs 'Bob'.

❓ Predict Output

advanced

Accessing a public attribute from outside the class

What is the output of this code?

Python

class Book:
    def __init__(self, title):
        self.title = title

b = Book('Python 101')
print(b.title)

A Python 101

B None

C AttributeError

D book.title

💡 Hint

Public attributes are accessible from outside the class.

The attribute 'title' is public and can be accessed directly using the object b.

❓ Predict Output

advanced

Effect of deleting a public attribute

What happens when you run this code?

Python

class Animal:
    def __init__(self, species):
        self.species = species

pet = Animal('Dog')
del pet.species
print(pet.species)

A AttributeError

B SyntaxError

C None

D Dog

💡 Hint

Deleting a public attribute removes it from the object.

After deleting pet.species, accessing pet.species raises AttributeError because it no longer exists.

🧠 Conceptual

expert

Understanding public attribute behavior in inheritance

Given this code, what is the output?

Python

class Parent:
    def __init__(self):
        self.value = 10

class Child(Parent):
    def __init__(self):
        super().__init__()
        self.value = 20

obj = Child()
print(obj.value)

A None

B 20

C 10

D AttributeError

💡 Hint

Child class overrides the public attribute after calling the parent constructor.

The Child class sets self.value to 20 after calling Parent's __init__, so obj.value is 20.

Practice

1. What is a public attribute in a Python class?

easy

A. An attribute that can be accessed and changed from outside the class

B. An attribute that is hidden and cannot be accessed outside the class

C. A method that runs automatically when an object is created

D. A special function to delete an object

Solution

1. Step 1: Understand attribute visibility

   Public attributes are designed to be accessed and modified from outside the class.

2. Step 2: Compare options

   An attribute that can be accessed and changed from outside the class correctly describes public attributes. Options A, B, and D describe other concepts.

3. Final Answer:

   An attribute that can be accessed and changed from outside the class -> Option A

4. Quick Check:

   Public attribute = accessible outside [OK]

Hint: Public means anyone can access or change it [OK]

Common Mistakes:

• Confusing public with private attributes
• Thinking methods are attributes
• Mixing up constructors with attributes

2. Which of the following is the correct way to create a public attribute name inside a Python class constructor?

easy

A. self->name = value

B. self.name = value

C. name = self.value

D. def name(self):

Solution

1. Step 1: Recall syntax for public attributes

   Inside __init__, public attributes are created by assigning to self.attribute_name.

2. Step 2: Check each option

   self.name = value uses correct syntax: self.name = value. Others are invalid Python syntax or wrong usage.

3. Final Answer:

   self.name = value -> Option B

4. Quick Check:

   Use self.attribute = value [OK]

Hint: Use self.attribute = value inside __init__ [OK]

Common Mistakes:

• Using def instead of assignment
• Wrong arrow syntax like self->name
• Assigning attribute to name instead of self.name

3. What will be the output of this code?

class Dog:
    def __init__(self, name):
        self.name = name

my_dog = Dog('Buddy')
print(my_dog.name)

medium

A. Dog

B. Error

C. my_dog

D. Buddy

Solution

1. Step 1: Understand attribute assignment

   The constructor sets self.name to the value passed, which is 'Buddy'.

2. Step 2: Print the attribute value

   Printing my_dog.name outputs 'Buddy'.

3. Final Answer:

   Buddy -> Option D

4. Quick Check:

   Print attribute value = Buddy [OK]

Hint: Print object.attribute to see stored value [OK]

Common Mistakes:

• Expecting class name instead of attribute value
• Confusing object name with attribute
• Thinking it causes an error

4. Find the error in this code that tries to create a public attribute age:

class Person:
    def __init__(self, age):
        age = age

p = Person(30)
print(p.age)

medium

A. The attribute should be assigned to self.age, not age

B. The print statement should be print(age)

C. The constructor is missing a return statement

D. The class name should be lowercase

Solution

1. Step 1: Check attribute assignment

   Assigning age = age only creates a local variable, not an attribute of the object.

2. Step 2: Correct attribute assignment

   It should be self.age = age to create a public attribute accessible outside.

3. Final Answer:

   The attribute should be assigned to self.age, not age -> Option A

4. Quick Check:

   Use self.attribute = value to create public attribute [OK]

Hint: Always assign attributes to self.attribute inside __init__ [OK]

Common Mistakes:

• Assigning to local variable instead of self.attribute
• Trying to print variable not attached to object
• Thinking constructor needs return

5. You want to create a class Car that stores the public attributes make and year. Which code correctly creates these attributes and allows access to them?

hard

A. class Car:
def __init__(self, make, year):
self.make = make
year = self.year

my_car = Car('Toyota', 2020)
print(my_car.make, my_car.year)

B. class Car:
def __init__(self, make, year):
make = self.make
year = self.year

my_car = Car('Toyota', 2020)
print(my_car.make, my_car.year)

C. class Car:
def __init__(self, make, year):
self.make = make
self.year = year

my_car = Car('Toyota', 2020)
print(my_car.make, my_car.year)

D. class Car:
def __init__(self, make, year):
self.make = make
self.year = year

my_car = Car('Toyota', 2020)
print(make, year)

Solution

1. Step 1: Check attribute assignments

   class Car: def __init__(self, make, year): self.make = make self.year = year my_car = Car('Toyota', 2020) print(my_car.make, my_car.year) correctly assigns self.make and self.year to the passed values.

2. Step 2: Check attribute access

   class Car: def __init__(self, make, year): self.make = make self.year = year my_car = Car('Toyota', 2020) print(my_car.make, my_car.year) prints my_car.make and my_car.year, which are valid public attributes.

3. Final Answer:

   class Car: def __init__(self, make, year): self.make = make self.year = year my_car = Car('Toyota', 2020) print(my_car.make, my_car.year) -> Option C

4. Quick Check:

   Assign and access via self.attribute and object.attribute [OK]

Hint: Assign attributes to self and access via object.attribute [OK]

Common Mistakes:

• Assigning attributes backwards (make = self.make)
• Accessing attributes without object prefix
• Mixing local variables with attributes